Pacing pass: unlock ladder, threat rate, economy values

Replace the everything-at--1 test setup with the real progression:
starting set is exactly drone/frigate/railgun_s/salvager; the ladder
runs destroyer+repair+armor at level 0, supports at 1, the quartz gate
(cruiser, railgun_m, afterburner, chip/hardened shortcuts) at 2,
battlecruiser at 4, battleship+railgun_l at 6, dreadnought at 8,
carrier+drone_hangar at 9, with unlock_requires edges cruiser ->
battlecruiser -> battleship -> dreadnought/carrier and railgun_m ->
railgun_l.

world.toml: threat_rate_formula 2*x + 0.15*x*x (below the player's
achievable military output early, crossing at the late boundary,
overwhelming by cycle ~24), starting_building_blocks 1000 -> 200,
expansion cost 200 -> 400 flat (placeholder until action item 4),
artifact_win_count 3 -> 5 (winning means choosing the artifact over a
schematic five times across ~7 cumulative offers).

Bug fix found during the pass: the building_block recipe carried no
unlock_at_station_level, and since building blocks appear in no
schematic's materials, implicit unlocking could never reach it - the
recipe was silently locked at game start. Now explicitly -1.

All values and derivations documented in content_design.md, "Pacing
pass - first values".

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DyCu8vwChKMbLJQ3xosYEN

docs/content_design.md

@@ -580,6 +580,65 @@ breakable). Round-3 knob changes: stabilizer range ×1.5→×1.3, and
 per-hull HP trims — battlecruiser 2700→2500, battleship 7500→7000,
 dreadnought/carrier 15500→19000.
 
+### Pacing pass — first values
+
+The mapping between station levels and boss cycles: at the intended
+push cadence (first set around cycle 2–3, roughly one per cycle from
+mid on), the destroyed set's level ℓ is reached around cycle ℓ+2. So
+level 2 ≈ the mid boundary, level 6 ≈ mid-late, levels 8–9 ≈ capitals
+with enough cycles left to ramp voidsteel production before late.
+
+**Starting set** (`unlock_at_station_level = -1`), per the starting-set
+rule (exactly enough to reach the first push): drone, frigate,
+railgun_s, salvager. Note: the building_block recipe must carry an
+explicit `-1` — building blocks appear in no schematic's materials, so
+implicit unlocking can never reach it (fixed in this pass; it was
+silently locked).
+
+**Unlock ladder** (level → unlocks; ← marks `unlock_requires`):
+
+| level | ships | modules | recipes |
+|---|---|---|---|
+| 0 | destroyer | repair_tool, armor_plates | |
+| 1 | | maneuvering_thrusters, sensor_booster | shortcut_steel_plate |
+| 2 | cruiser | railgun_m, afterburner | shortcut_control_chip, shortcut_hardened_steel |
+| 3 | | weapon_stabilizer | |
+| 4 | battlecruiser ← cruiser | weapon_primer, weapon_upgrade | |
+| 5 | | drone_bay | |
+| 6 | battleship ← battlecruiser | railgun_l ← railgun_m | |
+| 8 | dreadnought ← battleship | | |
+| 9 | carrier ← battleship | drone_hangar | |
+
+Level 0's pool has exactly three entries, so the first push offers a
+full dialog with no artifacts competing. Level 2 is the quartz gate:
+cruiser and railgun_m are the first schematics whose chains reach
+quartz (the shortcut recipes' outputs only become implicitly unlocked
+alongside them, so they cannot drop early).
+
+**Threat rate** `2*x + 0.15*x*x`, tuned against the factory-size curve
+with roughly half the player's output assumed military:
+
+| cycle x | rate (threat/s) | player military (≈ curve/2) |
+|---|---|---|
+| 2 | 4.6 | ~12 |
+| 6 | 17.4 | ~30 |
+| 15 | 63.8 | ~60 |
+| 20 | 100 | ~75 |
+| 24 | 134 | — |
+
+Below the player early, crossing at the late boundary, overwhelming by
+~24 — the endless-race shape from the progression rules. Typical wave
+at x=6 (30 s gap): ~520 threat ≈ two cruisers plus escorts; boss at
+x=15: ~3800 threat ≈ two and a half dreadnoughts.
+
+**Economy**: `starting_building_blocks` 1000 → 200 (minimal block loop
++ first shipyard ≈ 150, plus beginner slack); expansion cost 200 → 400
+flat (placeholder until the escalating formula, action item 4);
+`artifact_win_count` 3 → 5 with chance `0.05*x`: ~15–18 pushes in a
+winning run offer ~7 artifact options cumulatively, so winning takes
+choosing the artifact over a schematic five times — a real decision
+each time, and the win lands in the cycle 20–24 target window.
+
 ## Balancing targets (first pass, July 2026)
 
 The six root numbers for the balancing pass. Every derived value (threat